Vital signs are measures of the body's most basic functions, and are routinely used to help detect or monitor medical problems. The four primary vital signs monitored by medical professionals and health care providers are body temperature, blood pressure, pulse (heart rate), and respiration rate (rate of breathing). Body temperature can be measured with a thermometer, blood pressure with a blood pressure cuff and stethoscope, heart rate by simply counting the number of pulses in a minute, and respiration rate by simply counting the number of chest movements corresponding to breaths in a minute.
There have been prior attempts to gauge vital signs by wearing electronic devices outfitted with different kinds of sensors on the outside of the body. Such devices take different form factors (e.g., watch-type wristbands, straps, adhesive patches) and range in the kinds and sources of signals they measure, from an EKG that measures heart rate to a pulse oximeter on the finger tip that estimates peripheral blood oxygen saturation as a proxy for respiration rate. While indirect measures of respiration can be useful for gauging stress and fitness level (e.g., https://spire.io), they are not sensitive or accurate enough to depend on to save someone's life in cases such as respiratory depression, which a person might experience during an opioid drug overdose.
Changes in respiration rate can fluctuate rapidly, so a fast, accurate, passive, and objective measure is preferable for critical situations. Of the vital signs that may be measured for a patient in a hospital, however, respiration is the most subjective and indirect of assessments. While existing sensors may be used to monitor heart rate and temperature in an automated manner, monitoring respiration typically requires in-person attention and time intensive measurement by hospital staff. Nurses may count a patient's breaths while looking at their watches and then divide the elapsed time by breath count to assess respiration. This technique is often inaccurate. Also, because the required labor of performing manual measurements can be time consuming and costly, respiration measurements may not be taken as often as they otherwise would, either accidentally or intentionally, potentially leading to decreased quality of care.
Where speed and accuracy are required, direct measures of respiration would be far more reliable and would enable a more rapid and appropriate response to an emergency. In cases where there is not a life-threatening emergency, such as in sleep apnea, measuring breathing in a sensitive, fast, and accurate manner can still lead to more effective interventions and provide longer term health benefits. There is therefore a need for improved devices for monitoring a person's vital signs and methods that overcome some or all of the previously described drawbacks.